Fertilization sets into motion a pattern of normal development which has to a large extent been programmed by the events in gametogenesis. The hallmark of oogenesis is the diplotene lampbrush chromosome stage characterized by the extensive transcription of 5-10% of the genome. The experiments in this proposal are designed to identify the kinds of sequences transcribed on lampbrush chromosomes by in situ hybridization of cloned gene probes to the loop transcripts and to map in detail the structure and controlling sequences of a particular transribed loop. The physical organization of lampbrush chromosomes provides a powerful tool to assess the differences between active and inactive sequences. Features of both individual active sequences and the collective set of active sequences will be examined using light and electron microscope analysis of nuclease sensitivity and accessibility and immunocytochemical localization of associated proteins. Lampbrush chromosomes from chicken oocytes will be used as a new model system in these studies to take advantage of the small genome size and low representation of repetitious DNA. These studies will help elucidate the events governing normal development and help to clarify the elements involved in controlling gene expression and chromosome structure.